下列关于电场强度的两个表达式E＝F/q和E＝kQ/r2的叙述，正确的是
A．E＝F/q是电场强度的定义式，其中F是放入电场中的试探电荷所受的力，q是试探电荷的电荷量，它只适用于匀强电场
B．由电场强度的定义式E＝F/q得E与F成正比，与q成反比
C．E＝kQ/r2是点电荷场强的计算式，Q是产生电场的源电荷的电荷量，它不适用于匀强电场
D．从点电荷电场强度的计算式分析库仑定律表达式
，式中
是点电荷q1产生的电场在点电荷q2处的场强大小，而式中
是点电荷q2产生的电场在点电荷q1处的场强大小
答案：C
题目分析：
是电场强度的定义式，其中F是放入电场中的试探电荷所受的力，q是试探电荷的电荷量，该公式是普遍使用的，但是电场强度与库仑力和试探电荷量无关选项AB错。
是电场强度的计算式，Q是产生电场的源电荷的电荷量，电场强度大小有场源电荷和空间距离决定，适用于点电荷产生的电场，不适用与匀强电场选项C对。式中
是点电荷
产生的电场在点电荷
处的场强大小，选项D错。
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| The afternoon on December 25 in the waiting room, I was the nurse on duty. When I felt sad about having to 1 on Christmas Day, a woman and four small children showed up at my desk. "Are you all sick ?" I asked. "Yes." the woman said 2 and lowered her head. But when itcame to telling me about their 3 , things got a little surprising. They all seemed to be well and there was nothing 4 with their body. Why did they tell a 5 that they were all sick? I did not say anything but 6 that it might be a little time before a doctor could 7 them . The mother said, "Take your time. We can 8 here. It's so warm." When she finished the register chart, I noticed she didn't write down theiraddress- were they 9 ? I looked at the 10 around the Christmas tree. The children were excited and 11 to be healthy. The littlest one was pointing at the Christmas tree and said something to the mother. Then I wassure that they came here not because of 12 but only for warmth. I went back to the nurses' station and 13 the homeless family. The nurses, 14 about working on Christmas Day like me, turned to feel sorry for the family and decided to 15 .We bought delicious food in the hospital restaurant and 16 a big dinner for our guests. Weneeded 17 . So we put apples in a basket and collected candies and clothes. Just as we were seriously prepared to meet the physical needs of the 18 , our team worked to meet the needs of a family who just wanted to be 19 on Christmas Day. Later, as the family was to 20 , the youngest child ran to me and said, "Thank you very much.Good bye. " | ||||
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